Hydrocarbon production by secondary recovery



O 1969 c. D. WOODWARD 3 1 HYDROCAR BON PRODUCTION BY SECONDARY RECOVERYFiled June 29. 1967 United States Patent U.S. Cl. 166-245 10 ClaimsABSTRACT OF THE DISCLOSURE Conversion of a pattern pilot drive to asingle well line drive to sweep a production field by a meandering driveis disclosed, along with the prevention of reinvasion from adjoiningunexploited areas. This is accomplished during a direct in situcombustion operation initiated in an inverted 5-spot pattern by changingthe function of a production well, whereat breakthrough has occurred, tothat of an injection well, and initiating production at a selected wellof an adjoining pattern unit to continue the in situ combustion.Production at the other wells of the original pattern unit may becontained till breakthrough and then/or used as produced water disposalwells to prevent reinvasion, and the original injection well isconverted to a water disposal well also, thus maintaining a pressuregradient in the original pattern unit. These changes in function can befollowed consecutively as the in situ combustion operation proceedsthrough the pattern units of a production field.

Field of the invention This invention relates generally to theproduction of hydrocarbons from underground hydrocarbon-bearingformations, and more particularly, to a method for increasing theoverall production of hydrocarbons therefrom.

Description of the invention In the production of hydrocarbons frompermeable underground hydrocarbon-bearing formations, it is customary todrill one' or more boreholes or wells into the hydrocarbon-bearingformations and produce hydrocarbons, such as oil, through designatedproduction wells, either by the natural formation pressure or by pumpingthe wells. Sooner or later, the flow of hydrocarbons diminishes and/ orceases, even though substantial quantities of hydrocarbons are stillpresent in the underground formations.

Thus, secondary recovery programs are now an essention part of theoverall planning for virtually every oil and gas-condensate reservoir inunderground hydrocarbon-bearing formations. In general, this involvesinjecting an extraneous fluid, such as water or gas into the reservoirzone to drive the oil or gas toward production wells by the processfrequently referred to as flooding.

Another secondary recovery procedure employed for recovering theremaining hydrocarbons comprises the igniting and burning ofhydrocarbons in situ within the permeable underground formations,whereby hot gases are generated to force hydrocarbons in the formationtoward the production wells. While such in situ combustion has beenquite successful in secondary recovery operations, it has been much lessthan one hundred percent efficient because the combustion front tends toprogress through the formations along locally channeled paths from thearea of injection to the production area, thus bypassing substantialvolumes of the hydrocarbons in the formation, rather than sweeping thehydrocarbons as a bank from a broad area of the formation.

3,472,318 Patented Oct. 14, 1969 Summary of the invention It is anoverall object of the present invention to provide an improved in situcombustion procedure involving initially a well pattern arrangement toproduce almost all of the hydrocarbons remaining in place in theformation, by changing the function of the wells in the pattern atstrategic times to gain maximum control of the fire front.

An inverted five-spot pattern initiates the in situ combustion operationand proceeds until breakthrough occurs at one of the production wells.Upon breakthrough, this production well is converted to an air injectionwell, the original air injection well is converted to a water injectionwell for receiving the produced water, and the remaining pattern wellsare put on a standby basis, either being shut in completely or used forproduced water disposal, while production is initiated at a welladjacent the recently converted production to air injection well.

While this invention is applicable particularly to in situ combustion,it can be adapted readily to other forms of fluid drive for secondrecovery.

The objects, advantages and features of the invention will becomeapparent from a consideration of the specification in the light of thefigures of the drawing.

Brief description of the drawing FIG. 1 discloses four units of afive-spot pattern well arrangement, the third quadrant unit operating asan inverted five-spot pattern;

FIGS. 2 and 3 disclose the well arrangement of FIG. 1 during a laterphase of the in situ combustion operation, illustrating the change froma well pattern drive to a single well drive;

FIG. 4 shows a further change to a single well meandering operation;

FIGS. 5, 5a and 6 disclose also four units of a fivespot pattern wellarrangement showing the manner in which the direction of a pattern drivecan be controlled by means of the conversion of production wells toinjection wells;

FIG. 7 is a grouping of symbols used. throughout the drawing.

Description of the preferred embodiment As disclosed herein, it ispossible to change a pattern pilot operation into a single Well driveoperating in a meandering fashion to substantially completely sweep anunderground reservoir.

Referring now to the drawing, which schematically illustrates thepractice and advantages of my invention, there are illustrated a pair ofoperations observed in secondary recovery operations.

FIG. 1 discloses four units of a five-spot pattern well arrangement,wherein the third quadrant unit is operating as an inverted five-spotpattern, the figure depicting in dotted outlines an ideal burnt out areafor the inverted five-spot pattern, while the cross hatching indicatesthe actual burnt out area at breakthrough at one of the interior wellsof the pattern.

In the inverted five-spot pattern, the corner wells of each pattern unitare production wells while the central well is used for injection.Throughout the figures of the drawing, the same symbols will bemaintained as follows: the open circle to indicate a well site, a solidcircle to indicate a production well, a crossed circle to indicate ashut in well, a single head arrowed circle to indicate a water injectionwell, and a double head. arrowed circle to indicate an air injectionWell.

FIG. 2 discloses the conversion of the pattern pilot of FIG. 1 into asingle well drive, wherein the production Well at breakthrough in FIG. 1now has been converted into an air injection well, the former airinjection well is now a water injection well to receive the waterproduced from the underground formation, and an interior well of thefive-spot pattern adjacent the production well on breakthrough in FIG. 1has been put on production. This well has been selected for productionassuming that the drive is toward the northeast, but any of the otherwell sites could be chosen to direct the pattern flood in thatdirection, as will be developed further.

FIG. 3 discloses a later state of the production drive patterns of FIGS.1 and 2, wherein the single well drive is meandering toward thenortheast to the corner well indicated as No. 1, the production well atbreakthrough in FIG. 2 having been converted to an air injection well,the former air injection well to a water injection well, while the waterinjection well of FIG. 2 is indicated as remaining so, although it couldbe closed in as are the corner wells of the original pattern.

Upon breakthrough of the fire flood at well No. 1, as indicated in FIG.3, production can be initiated at either wells Nos. 2 and 3 or at anyother of the adjacent well sites, depending on the direction of choice.In FIG. 4, the production well at breakthrough at No. 1 is converted toa water injection well to prevent reinvasion while the previouslyfunctioning air injection well of FIG. 3 remains so and the two waterinjection wells maintain their same function. If production at well No.2 has been chosen, then the additional sweepout area indicated by thedifferent angled cross hatching would result. Upon breakthrough of thefire flood at either wells Nos. 2 or 3, depending on the choice forproduction, then these wells could be converted to air injection wellsin the manner disclosed basically in FIG. 2 and a drive commencedtowards the newly selected production well, e.g. No. 4, to complete thesweepout in the first three quadrants of the pattern. In the samemanner, the sweepout of the fourth quadrant pattern can be completed.Alternatively, the pattern of FIG. 3 can be applied along paralleldiagonals of a five'spot pattern production field.

Although in FIGS. 2, 3 and 4, the former production wells of FIG. 1 areshown as shut in, they are classified as stand-by for either waterinjection, if necessary to control the pattern as will be discussedbelow, or they could be maintained on production until breakthroughoccurs thereat and converted to water injection wells to preventreinvasion of the pattern from adjacent areas not yet swept out.

Tests were made to observe the principles disclosed above in a reservoirin south Texas, the reservoir data being substantially as follows:

Depth ft 1575 Average net sand thickness ft 18 Porosity percent 32.7 Oilsaturation do 38.0 Permeability to air, 1nd 1610 API gravity 20.9

An air injection well was drilled between two existing wells, one aformer producer and another a former water injection well. Serviceinstallations were made, these latter two wells were equipped asprincipal producers, and air receptivity was established at the airinjection well. Ignition of the in place crude was accomplished withspontaneous ignition chemicals. During the life of the experiment, leaseoil production more than doubled in the four months after ignition andat the termination of the project, the former producer well was pumpingand flowing under normal operating conditions at a rate better thanfifteen times the settled production rate prior to ignition. Combustiongas showed up at most of the wells on the leases sometime during theproject, with the closest production wells being affected to a greaterdegree. Five months after ignition, a test well was drilled behind thereaction zone, showing the entire vertical section as burnedsubstantially clean, the rate of advance of the reaction zone being inexcess of 0.5 ft./day.

Bottom hole temperature, F.

Eight months after ignition, the fire front arrived at the formerproducer well. This hot production well was shut in and converted to anair injection well to determine if the point of air injection could bemoved while maintaining the combustion process. Gas analyses and gasproduction from surrounding wells indicated the burn was sustained andpropagated during and after the change.

This experiment demonstarted that a production well which has beenovertaken by athermal reaction zone can be converted to an air injectionwell and the burn successfully sustained and advanced in the reservoir.Thus, a single well line drive can be established in a field by asequence of production and injection at a given well, or alternatively,a field can be exploited by allowing the reaction zone to meander aboutin a reservoir with the abandoned air injection well available for waterdisposal and reinvasion control.

Referring now to FIGS. 5, 5a and 6, there is shown how the disclosedinvention can be used to control the direction of the drive consideringdifferent permeabilities of the reservoir. In FIG. 5, a pattern pilothas broken through at one of the production wells on the outside edge ofa four unit, five-spot pattern in a direction opposite to that desired,e.g. toward the northeast quadrant. To alleviate the problem, theproduction well suffering breakthrough is now converted into a waterinjection well to continue the drive toward the other production wellsof the pattern unit, until breakthrough is achieved in the desireddirection. If breakthrough occurs at one of the boundary patternproduction wells, then it too can be converted from a production well toa water injection well, as indicated in FIG. 6. In this figure, there isdisclosed how the sweepout pattern of FIG. 5 has been controlled bychanging the drive direction toward the northeast quadrant. In FIG. 5a,the breakthrough well in production in FIG. 5 has been converted into awater injection well to prevent reinvasion from adjoining patterns andforce the sweepout pattern in the opposite direction, with breakthroughoccurring at an inside boundary production well. The function of thiswell is changed to an air injection well, the former air injection wellin the center of the first five-spot pattern being exploited beingconverted into a water injection well, and production beginning at oneof the Wells adjacent the pattern in the direction desired. This patternof FIG. 6 corresponds to that in FIG. 2 but differs therefrom by theconversion of the corner production wells of the pattern to a waterinjection well upon respective breakthroughs.

FIG. 7 is self explanatory and indicates the various symbols used in thepreceding figures of the drawing.

Thus, it has been shown and described how a pattern pilot drive isconverted into a single well line drive to sweep a production field by ameandering drive, preventin-g reinvasion from adjoining unexploitedpatterns and providing a solution for water disposal.

Obviously, other modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

1. A method of producing hydrocarbons from an undergroundhydrocarbon-bearing formation involving an injection well and a pair ofwells immediately adjacent thereto and to each other and in linetherewith and penetrating into said formation, at least one of said pairof wells being a production well, which comprises introducing acombustion-supporting fluid into said formation via said injection welland initiating in situ combustion thereat, producing fluids includinghydrocarbons from said formation via the well closer to said injectionwell and maintaining producing fluids therefrom until the front of saidin situ combustion arrives thereat, thereupon, ceasing producing fluidstherefrom and commencing introducing said combustion-supporting fluidthereinto and ceasing introducing said combustion-supporting fluid intosaid formation via said injection well and beginning the introducing ofwater into said formation via said aforementioned injection well whileproducing fluids including hydrocarbons via the other of said pair ofwells until breakthrough of said front thereat.

2. In a method of producing hydrocarbons as defined in claim 1, saidwells being included in a pattern of wells in a producing field, thesteps of consecutively changing a production well at which said frontappears to an injection well thereof, and converting an immediatelypreceding injection well for said combustion-supporting fluid into aninjection well for water, said water being prodnced with said fluidsincluding hydrocarbons from the production well.

3. In a method of producing hydrocarbons as defined in claim 2, saidwells being part of a series of five-spot well patterns.

4. In a method of producing hydrocarbons as defined in claim 3, thesteps of consecutively changing the functions of said wells beingapplied along parallel diagonals of the producing field pattern.

5. A method of producing hydrocarbons from an undergroundhydrocarbon-bearing formation involving a centrally located injectionwell surrounded by production wells located at the vertices of aquadrilateral and penetrating into said formation which comprisesintroducing a driving fluid into said formation via said injection well,producing fluids including hydrocarbons from said formation via theproduction wells defining said quadrilateral until breakthrough of saiddriving fluid occurs at one of said production wells, thereupon ceasingintroducing said driving fluid into said formation via said injectionwell and producing fluids including hydrocarbons from said productionwell where said breakthrough of said driving fluid has occurred andconverting said last mentioned production well into an injection wellfor said driving fluid, and initiating the producing of fluids includinghydrocarbons from a well adjacent said injection well converted fromsaid production well where said breakthrough of said injection fluid hasoccurred.

6. In the method of producing hydrocarbons as defined in claim 5, thestep of converting the original injection well for driving fluid into aninjection well for water, said water being produced with the fluids fromthe production wells.

7. In the method of producing hydrocarbons as defined in claim 6, theadditional steps of respectively ceasing producing fluids includinghydrocarbons upon breakthrough of said driving fluid at a productionwell and converting the same to an injection well, and initiatingproducing fluids including hydrocarbons from an adjacent well until saidhydrocarbon-bearing formation has been swept clean.

8. A process for recovering hydrocarbons by in situ combustion from agas pervious underground hydrocan hon-bearing formation by exploitationthrough a well pattern penetrating thereinto wherein a central well islocated within a ring of a plurality of diametrically positioned wellscomprising:

(a) injecting air into said central well and initiating in situcombustion of hydrocarbons there-at, thereby forming a high temperaturecombustion front which moves away from said central well,

(b) simultaneously producing fluids including hydrocarbons from saidformation via said diametrically positioned wells until said hightemperature combustion front breaks through at a well thereof, and

(c) ceasing producing fluids and thereafter commencing injecting waterinto the production well Where said combustion front has broken throughwhile continuing said in situ combustion of formation hydrocarbons andproducing fluids including hydrocarbons from said remainingdiametrically positioned wells until breakthrough of said front thereat,thereupon converting selected ones of said remaining wells to waterinjection wells and at least one of said remaining wells to an airinjection well and initiating the production of fluids includinghydrocarbons from a well adjacent said last mentioned well.

9. In the process as defined in claim 8, the additional step of (d)injecting a pressurized fluid into said central well to maintain apressure gradient outwardly from the zone burned out by in situcombustion whereby the air injection of step (c) is restricted to thehydrocarbon-bearing formation outside of said zone.

10. A process in accordance with claim 9 wherein said well pattern is afive-spot well pattern located within a much larger pattern of wells ina producing field, and wherein said steps are applied to a series ofadjoining wells arranged in a series of such well patterns within saidlarger pattern.

References Cited UNITED STATES PATENTS 2,798,556 7/1957 Binder et a1.166-9 2,841,375 7/1958 Salomonsson 166-11 X 3,113,617 12/1963 Oakes166-9 3,143,169 8/1964 Foulks 166-9 3,150,715 9/1964 Dietz 166-11 X3,153,448 10/1964 Dew et al. 16611 X 3,253,652 5/1966 Connally et al.166-11 X 3,256,934 6/1966 Nabor et al. 1-669 3,270,809 9/1966 Connallyet a1. 1669 STEPHEN J. NOVOSAD, Primary Examiner US. Cl. X.R.

